 grammar {
 
 start = element library {library-content}
 
 library-content =
   element book { book-content } +
 
 book-content = 
     attribute id { text },
     attribute available { text },
     element isbn { isbn-content },
     element title { title-content },
     element author { author-content }+,
     element character { character-content }*
 
 isbn-content = text
 
 name-content = text
 
 born-content = text
 
 died-content = text
 
 qualification-content = text
 
 title-content = 
   attribute xml:lang { text },
   text
 
 author-content =
   attribute id { text },
   element name { name-content },
   element born { born-content }?,
   element died { died-content }?
 
 character-content =
   attribute id { text },
   element name { name-content },
   element born { born-content }?,
   element qualification { qualification }
 
 }
